Multi-channel cooling die

ABSTRACT

A cooling die for extruding of high moisture extrudate food products having a cooling die body in which are defined a plurality of extrudate flow channels extending between an inlet end of the cooling die that is attachable to an extruder and outlet end for delivery of cooled-down extrudate, and coolant cavities located in heat-exchanging communication with the extrudate flow channels and connectable to a source of coolant, characterized in that the cooling die body consist of a plurality of thick plates having first and second channels extending between and opening at the planar surfaces of the thick plates, and that the plurality of thick places are stacked and fastened together such that the opening of the first and second channels of adjoining plates are respectively aligned with one another, whereby the first channels form said plurality of extrudate flow channels and the second channels form a plurality of discrete coolant channels extending through the length of the cooling die body.

FIELD OF THE INVENTION

This invention relates to cooling dies for use in association with foodextruders in the manufacture of texturised protein food products, and aperforated die plate for use at the cooling die outlet.

In particular, the present invention relates to a cooling die for use inthe manufacture of an extrude food product that has the appearance offibrous meat pieces such as fish, chicken, lamb or beef. The cooling dieis attachable to the outlet of an extruder which may contain one or morescrews and feeds molten extrudate to said cooling die at a temperaturebetween 110° and 180° C.

BACKGROUND OF THE INVENTION

Various protein texturisation processes have been used for some time inthe manufacture of various food product, such as in the manufacture ofsausages, cheese curds, mozzarella processed cheeses, bakery products,tofu, kamaboko, meat analogs and seafood analogs. A fibrous texture maybe obtained by various means, including extrusion cooking at lowmoisture levels (typically 10-30% by weight).

Extrusion cooking at high moisture levels (e.g. typically 30 to 80%water by weight) is a relatively new technique which is finding usemainly in the field of texturisation of protein food products.

High moisture extrusion cooking has been discussed as a means ofrestructuring various natural protein sources, such as fish mince,surimi, de-boned meats, soy flours, concentrates, cereal flours, dairyproteins and the like, in order to obtain cohesive fibrous or lamellarstructures (e.g. see “New Protein Texturisation Processes by ExtrusionCooking at High Moisture levels” by J C Cheftel et al, Food Reviewsinternational, 8 (2), 235-275 (1992) published by Marcel Dekker, Inc.).

Unlike low moisture extrusion cooling, high moisture extrusion cookingrequires the use of cooling dies for cooling, gelling and/or solidifyingthe food product issuing from the food extruder. A cooling diedissipates the thermal and mechanical energy accumulated in the foodmix, increases the viscosity of the mix, and prevents product steamflash at the die outlet

The concept of extruding cereal, meat or other protein blends at highmoisture through an extruder and then passing the extrudate through anattached cooling die, so that product exits the cooling die attemperatures not exceeding 100° C. (typically about 80° C.), is not anew one. This cooling of the product is quite important in order toeliminate expansion of said product as a consequence of steam flashing,amongst other things. There are numerous patents and articles discussingthis subject, including discussions of die design in particular.

It is understood that texturisation of the protein food product takesplace during cooling as a result of lamellar flow in the die.

Three main types of cooling dies are known for use in this field oftechnology/application. Most commonly known are elongated rectangularcooling dies. A rectangular cooling die has a long rectangular prismatichousing in which is received a rectangular duct extending along thelength of the die. The regions surrounding the rectangular cavity (duct)are cooled with water thereby enabling the extruded food product passingthrough to be cooled. Cooling dies may also be cylindrical with aninternal cylindrical cavity extending along the length thereof. Such acooling die functions in much the same manner as a rectangular coolingdie. There are annular cooling dies in which the internal cavity has anannular cross-section defined by an inner core and an outer cylinder.The inner core and outer cylinder are cooled, thereby enabling the foodproduct passing through the cavity to be cooled.

One problem with known cooling dies is that, as portions of the foodproduct come in contact with the coded surfaces of the die, theseportions become thicker, tend to stick to the surface of the die andslip at a lower rate than internal sections of the product Accordingly,velocity gradients and shear forces develop which may causeinconsistencies in the food product and problems with the smoothcontinuous operation of the cooling die and extruding apparatus. This isa particular problem where the dimensions of the cooling die cavity(e.g. height, width and/or length) have been increased so as to achievegreater throughput of extruded products.

Another problem with known cooling dies is that they effectively cause a“bottle-neck” in the extrusion process. Typically, the capacity of acommercial cooling die is about 100 kilograms per hour, so that productoutput is limited to this value.

Whilst this extrusion rate has been found to be desirable in order toachieve a commercially acceptable product, it is desired to have greaterproduct output rates to increase yields. The production of high moistureextruded products at manufacturing outputs of up to 200 kg/hr usingsingle channel cooling dies has also been documented. However, extrudedproducts manufactured at these rates tend to be of lower quality and/orconsistency than those manufactured at lower rates. Production rates inexcess of 200 kg/hr are much more difficult to achieve, due to thephysical limitations of known cooling die designs.

The output of a cooling die is determined by a multitude of factors, onemajor factor being the capacity (of volume) of the cooling die cavity(or channel) which is determined by the cross-sectional area and thelength of the die cavity, it increased production rates are required,one has the choice of increasing the cross-sectional area or die lengthor both. This strategy however may be limiting. For instance, thecross-sectional area of the die cavity is largely determined by thedesired product characteristics. Also, increasing the cross sectionalarea would typically increase the amount of time required to cool theproduct. It may result in inconsistencies in the product due to theouter portions of the extruded product cooling much faster than theinner portions. Altering the die shape may give a product not meetingdesired visual parameters. Increasing the length of the cooling die alsohas limitations due to the fact that the pressure drop along the die isproportional to the length of the die. Increasing the pressure dropalong said cooling die will decrease output of the die or requireincreased extruder capabilities.

Attempts have also been made to increase the capacity of cooling diesthrough the use of higher flow rates with cooling dies of greatercross-sectional areas. This measure necessitates longer cooling dies.This has a number of adverse consequences. For instance, longer coolingdies increase the likelihood of inconsistencies arising in the foodproduct and structure blockages occurring in the cooling die. Also, suchdies obviously take up more area or floorspace of the production plant,which in turn increases costs.

Japanese patent application No. 4-214049 (publication No. 6-62821)discloses a multi-channel cooling die which is used in the extrusion ofthin, thread-like food products from high moisture content proteinaceousraw materials. The cooling die is essentially constructed like a typicalshell-and-tube heat exchanger, wherein the shell covers at the axialends of the cylindrical shell are replaced with purpose built endplates. The inlet end plate is flanged to the extruder's die plateholder, while the other end plate is similar in layout to the stationarytube sheet of the heat exchanger, i.e. a multiple-orifice plate in whichthe ends of the plurality of inner tubes are wedged and supported.

The plurality of thin-walled inner tubes employed in such typo ofcooling die ensure efficient cooling at higher through-put rates ofextrudate. It is said that the individual tubes possess high pressureresistance thereby enabling processing of greater amounts of rawmaterials as compared with conventional, single cavity cooling dies.

One serious shortcoming of such type of cooling die is the need to use“pigs” or long rods for cleaning the individual inner tubes throughwhich the extrudate flaws during processing. The smooth surface of thetubes can be damaged during the cleaning process (due to their length),which may result in irregular loading of individual tubes from theextruder as a consequence of increased surface roughness (and backpressure) at individual tubes. Also, in case one of the tubes is damagedto an extent that it no longer provides a flow path for the moltenextrudate. It is necessary to replace the entire cooling die or performa time and labour intensive replacement process: because the individualtubes are received in airtight manner at the end plates of thecylindrical shell, all tubes have to be removed and refitted in order toexchange any one of them.

SUMMARY OF INVENTION

The present invention is directed to providing a cooling die for usewith a food extruder, which enables greater manufacturing output withoutsubstantially increasing the cross-sectional area or length of theextrudate flow cavity, when compared to single cavity cooling dies usedin the art, by providing a multi-channel cooling die which addressessome or all of the disadvantages perceived to exist with shell-and-tubetype cooling dies.

The present invention also seeks to provide a cooling die whichincorporates means to enable extrusion of extrudates of varyingcross-sectional shapes/sizes without the need to stop extrusion of theproduct.

According to a first aspect of the invention there is provided a coolingdie for extruding of high moisture extrudate food products, having acooling die body in which are defined a plurality of extrudate flowchannels extending between and inlet end of the cooling die that isattachable to an extruder and an outlet end for delivery of cooled-dawnextrudate, and coolant cavities located in heat-exchanging communicationwith the extrudate flow channels and connectable to a source of coolant,characterised in that the cooling die body consist of a plurality ofthick plates having a plurality of first and second bores extendingbetween and opening at the planar surfaces of the thick plates, and inthat the plurality of thick plates are stacked plane-parallel andfastened together such that the opening of the first and second bores ofadjoining plates are respectively aligned with one another, whereby thefirst bores form said plurality of extrudate flow channels and thesecond bores form a plurality of discrete coolant channels extendingthrough the length of the cooling die body.

Such type of cooling die layout has a number of advantages over theabove described shell-and-tube cooling die. Firstly, the stackedarrangement of individual plate members allows assembly of cooling diesof varying length by removing or inserting individual plate members,thereby providing adaptability to different cooling requirements of theextrudate. Secondly, the extrudate flow channels are easier to cleanwithout risk of damage, as the die body can be easily dismantled therebyto provide access to the relatively short bores formed in the individualplate members. Conventional sealing elements and/or mean are providedbetween the individual plate members thereby to ensure formation of leakproof and pressure resistant channels extending between the axial endsof the die body assembly once the plates have been stacked and securedto one another.

There are numerous ways in which the stack of plate member can besecured to form a unitary die body, including fastening of adjoiningplate members through suitable fasteners (i.e. recessed screw/nutfasteners), clamping of the entire stack of plates between end plateswhich are tensioned using threaded rods or the like, and similar. Also,alignment elements may advantageously be present between each pair ofadjoining plates to ensure coaxiality of the openings of the first andsecond bores of the plates with one another. There are numerous ways inwhich the plates can be fastened and aligned with one another, as is thecase with sealing mechanisms to provide leak-free passage of extrudateand coolant through the respective channels in the cooling die body.These am known to the competent tool making engineer.

In a preferred form of cooling die in accordance with the presentinvention, there are provided a coolant supply and a coolant dischargeend plate at axially opposite ends of the cooling die body, wherein theend plates include manifold conduits for supplying or dischargingcoolant to/from the coolant channels of the die body, as the location ofthe end plates dictate. Advantageously, the manifold conduitscommunicate with a common coolant supply/discharge armature fixed to therespective end plate for connecting the manifold conduits to a source ofcoolant or a receptacle reservoir, as the case may be. One manifoldconduit may be arranged to supply or receive coolant from one or aplurality of coolant channels, the latter being grouped in fluidcommunication in sets of two or more channels in order to decreaseindividual connection points between manifold conduits and coolantchannels. Extrudate flow bores will also be present in both end plates,to allow entry and exit of extrudate into thee cooling die body plates

The extrudate flow channels of the die body may be orientated in anysuitable manner and extend either axially through the body or in ahelical pattern or the like. In case of co-axially arranged extrudateflow channels, these may be arranged in a regular or irregular patternof rows or columns, in a preferred embodiment the extrudate flowchannels being located radially about the longitudinal axis of thecooling die body.

In a preferred form, the cooling die longitudinal axis is disposed inalignment with the axis of the extruder to which the former is connectedin use.

In one preferred form, the cooling die body contains twenty-four (24)extrudate flow channels equidistantly spaced about the axis of the die,The arrangement of extrudate flow channels in a pattern that isequidistantly spaced about the axis of the die with each channel havinga cross-section opening which extends substantially in radial direction,has several advantages, including efficient use of space, ease ofmanufacture of the individual plate members and optimal packagingdensity. This arrangement also allows to interleave one or more coolantflow channels between neighbouring extrudate flow channels.

In a preferred form, the extrudate flow channels will have an oblong orlong-hole cross-section (i.e. rectangular shape with rounded short ends)thereby to prevent sharp edges in which extrudate could deposit andadhere. Each extrudate flow channel will have a radial height which issubstantially greater than the width thereof (i.e. dimension inperipheral direction of the cylindrical die plates). The height of eachchannel is preferably greater than 20 mm and typically about 70 mm,whereas the width would be about 4 mm or more, preferably about 8 mm. Itwill be appreciated that other cross-sectional shapes may be usedinstead of substantially rectangular cross-sections, bearing in mindthat different cooling requirements apply to different cross-sectionalshapes of extrudate flow channels.

A noted above, it is preferred to have an alternating arrangement ofcoolant and extrudate flow channels, wherein it is advantageous to havetwo or more radially spaced coolant channels extended between twoneighbouring extrudate flow channels, thereby to increase heat transferfrom the extrudate into the coolant. A radially symmetrical arrangementof coolant and extrudate flow channels about the longitudinal axis ofthe cooling die body is preferred.

Due to the operating pressures and temperatures, the thick plates thatmake up the cooling die body will be machined from solid metal, e.g.Stainless steel, aluminium and the like.

In a further development of the present cooling die invention, there isincorporated an extrusion die plate at the outlet end of the cooling diebody downstream of the coolant discharge header plate (also referred toas a distribution end plate) the extrusion die plate having a pluralityet discharge orifices of predetermined shape and configuration that aregrouped and arranged to be selectively bought in axial alignment withpredetermined ones of the extrudate flow channels thereby to enableextrusion of cooled-down extrudate bands having selected ones ofdifferent cross-sectional shapes in accordance with the dischargeorifice shape.

Incorporation of such type of cooling die extrusion plate allowsextruding of extrudate bands having selected cross-sectional shapesthrough a single extrusion plate by simple repositioning of theextrusion die plate at the cooling die outlet end. This in turn enablesto increase efficiency of the extruder cooling die assembly, as the needto shut down the extruder (often for a few hours) in order to exchange adie extrusion plate is avoided.

In a preferred form of extrusion die plate, the number of dischargeopenings is a natural multiple of the number of extrudate flow channels,wherein the respective multiples are grouped together such that onegroup can be brought into alignment with the extrudate flow channels,whilst the other group is offset therefrom, the first group of dischargeorifices having a cross-sectional shape that is different from that ofthe second group. Alternatively, the discharge orifices may all have thesame cross-sectional shape and selected ones of the openings may betraversed by a predetermined number of cutting blades, wires or websthereby subdividing the respective orifice into a correspondingplurality of smaller openings.

Preferably, the extrusion die plate is arranged to move between a firstposition in which the orifices featuring the cutting elements align witha selected number of the extrudate flow channels, and a second position,in which the orifices featuring the cutting elements do not align withthe channels. A benefit of this embodiment is that one can selectivelyhave extruded product exiting the cooling die either as wide strips(i.e. where the extrusion die plate orifices have an oblong orrectangular cross-section corresponding to that of the extrudatechannels) or as “strings” (for instance, having squarishcross-sections), simply by moving the die plate (or screen) from thefirst position to the second position. Rapid change of the extrusion dieplate position at the outlet of the cooling die results in lessdown-time and less wastage of product, which thereby results inconsiderable cost savings.

When the multi-channel cooling die is a “radial” cooling die (havingextrudate flow channels arranged equidistantly about the axis of the diebody and each having a substantially radial extension), extrusion thedie plate is preferably disc-shaped and rotatable about the central axisof the assembly. The circular plate may be moved between the firstposition and the second position simply by rotating it. The plate mayhave sets of orifices featuring cutting elements adapted to align witheach of the extrudate flow channels and “open” orifices between each ofthe sets of apertures featuring cutting element. When the set of cuttingelements are aligned with the extrudate flow channels, the productexiting the cooling die will be cut by the cutting elements so as toform “strings” of extruded product

Where, for example, the cooling die has twenty four equi-peripherallyspaced extrudate flow channels, the extrusion die plate may have acorresponding twenty four orifices with cutting elements and twenty four“open” orifices. By rotating the plate or screen through 7.50°, theplate is moved from the first position, in which the set of aperturesfeaturing cutting elements align with the extrudate flow channels, andthe second position, in which the “open” apertures align with thesechannels.

Alternatively, in the case of a twenty four channel cooling die, thecooling die extruder plate or screen may have twelve apertures featuringcutting elements and twelve “open” apertures. In this case, anadditional “shutter” plate would be preferably located at the inlet endof the stacked die body, to selectively shut 12 of the extruder flowchannels so that product would only be permitted to pass through theother twelve of the channels; the apertures featuring cutting elements,or the open apertures would, selectively, be in alignment with theseopen twelve channels. The apertures featuring cutting elements or the“open” apertures which are not in use would be in alignment with thosechannels through which no product is passing,

As will be appreciated, provision of such variable cooling die extruderplate requires that the cooling die end (or coolant distribution) platesat each and of the cooling die body are designed with axially extendingsack holes for the coolant channels of the die. The sack holes are thenin communication with the radially extending bores that terminate in theperipheral surface at suitable fitting that enable connection to coolantmanifold lines. Accordingly, the cooling fluid will not flow axiallypast the end plates of the cooling die.

The cooling die may further be associated with a cutting apparatus thatincludes cutting means for cutting the strips or lengths of theextrudate exiting the cooling die extrusion plate into pieces of desiredlength. This cutting means may be a rotatable blade. Preferably, thecutting apparatus further includes means for varying the speed at whichthis blade rotates. By varying this speed, the length of pieces of theproduct being cut can thereby also be varied.

A preferred embodiment of the invention is described below withreference to the accompanying drawings and by way of example only.Further advantages and preferred features of the invention are discussedthere also.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan side view (schematical) of a first embodiment of thecooling die showing its overall layout;

FIG. 2 is a cross-section of the cooling die of FIG. 1 at line A—A,showing detail of the cooling fluid path at the end (coolantdistribution) plate of the cooling die plate stack;

FIG. 3 is a cross-section of the cooling die of FIG. 1 at line B—B.showing the arrangement of extrudate flow channels and the coolant flawbores;

FIG. 4 is a plan side view (schematic) of a further embodiment of acooling die in accordance with the invention, incorporating a coolingdie extrusion plate;

FIG. 5 is an enlarged detail view of FIG. 4 at the cooling die extrusionplate end;

FIG. 6 is an elevation of the outlet and of the cooling die of FIG. 4;

FIGS. 7 and 8 are a plan view and longitudinal section, respectively thecooling die extrusion plate shown in FIGS. 4-6

DETAILED DESCRIPTION

In order to produce extruded food product such as fibrous meatanalogues, one requires an extruder with the ability to impart shear andpressure on the ingredient formulation and convey said material to thecooling die. The extruder may contain one or more screws. These are wellknown and will not be described here.

A cooling die assembly, in accordance with the invention, for use al thedelivery end of a high moisture proteinaceous food extruder, is shownschematically in FIG. 1. The die assembly 10 essentially comprises amulti-piece die body 12 consisting of a plurality (here: 18) ofdisc-shaped thick steel plates 14 of identical layout, a coolant (i.e.cooling fluid) inlet header (or distribution) plate 16 at the axialinlet end of the die body 12, a coolant outlet header (or distribution)plate 18 at t axial outlet end and connection and transition structuresfor securing die 10 to a receptacle flange at the extruder outlet(notionally represented at dotted line 11) and clamping of theindividual die body plates 14 together.

A total of twenty-four extrudate tow channels extend axially andparallel to one another between the inlet end of die body 12 and theoutlet end thereof, partial sections of the extrudate flow channelsbeing defined by bores or “part channels” extending through each of theplate members 14 that make up die body 12. FIG. 3 illustrates incross-section one of the cooling die plates 14 which, when stoked andclamped together, form cooling die body 12. The bores that make up theextrudate flow channels are identified at 20. The cross-section of theextrudate flow channels 20 is identical and about rectangular withrounded edges (or in the form of long holes/oblong). The major dimensionor height of the channel 20 extends in a substantially radial directionfrom the central axis of to die body 12, and is at least 2.5 times thewidth thereof. The twenty-four extrudate flow channels 20 areequi-distantly spaced in circumferential direction of the plate members14.

As can be further gleaned form FIG. 3, a plurality of bores 22 aremachined into and extend through each die body plate 14 in a regularpattern an located between neighbouring extrudate flow channels 20, atotal of four radially spaced apart bores being provided per row. Whenthe individual die plates 14 are stacked, these bores 22 form aplurality to coolant flow channels which extend parallel to one anotherbetween the product inlet and outlet ends of die body 12,

As noted above, at each end of cooling die body 12 are located coolingfluid (i.e. coolant) header plates 16, 18 which provide the terminalends for the coolant flow channels 22 at the product inlet and outletsides of the die assembly 10. These are in essence mirror-identical toone another, the only difference being their location with respect toextrudate flow through the cooling die, i.e. inlet and outlet endplates. Because these end plates 16, 18 also perform a function ofdistributing coolant from a single source to the individual coolant flowchannels 22 of the die plate assembly 12, or receiving such coolant,they are here also referred to as distribution (end) plates 16, 18. Onlyone will be described in more detail.

As can be seen from FIG. 2, which illustrates schematically and incross-section one such coolant header plate 16, a total of twenty-fourradially extending coolant supply/discharge bores 24 extend fromrespective coupling armatures 25 located at regular intervals along theperipheral surface of the disc-shaped distribution plate 16 towards thecentre thereof and terminate with distance thereof. Eachsupply/discharge bore 24 is in fluid communication with a total of fourcoolant flow bores 22′ machined from one side only axially into thedistribution plate 3. The sack bores 22′0 are shaped to correspond incross-section, arrangement pattern and location with the coolant flowchannels 22 provided in the cooling die plates 14 (compare FIG. 3), withwhom they align when the plates 14, 16, 18 are stacked.

As can be further seen in FIG. 2, the distribution plate 18 (as well as18) also has twenty-four long holes 20′ which are arranged in a patternand have a size corresponding to that of the extrudate flow channels 20of the cooling die plates 14 (and cooling die body 12) with whom thesealign when the die is assembled.

A coolant distribution manifold structure 26 incorporates a total oftwelve coupling armatures 27 fastened to a common supply/discharge tube29. Tube 29 is secure/fixed vie bracket 34 to the upper side ofdistribution plate 16 (and 18) or any other suitable component of thecooling die assembly. A total of twenty-four coolant lines 28 connectthe coupling armatures 25 and 27 thereby to allow manifold feeding ofcoolant through a single inlet to the twenty-four individual coolantsupply ducts 24 at the inlet end plate 16. The same configuration ispresent at the outlet end distribution plate 18. It is immediatelyapparent that direction of flow of coolant can be either in line withthe direction of extrusion of materials passing through the extrudateflow channels 20 or in counter-flow from the product outlet end to theinlet end of the cooling die assembly 10. In other words, the fluiddistribution plates 16 and 18 also serve as “entrance” and “exit” gatesof the extrudate product, as well as for the distribution of coolingfluid.

Not shown in any detail in the accompanying drawings, it is evident thatsuitable alignment elements/members will be provided on the individualcooling die plate members 14 thereby to allow co-axial alignment of therespective bores 20, 22 which make up the extrudate flow channels andcoolant flow channels. By the same token, suitable sealing elements willbe provided thereby to ensure leak-free connection between the bores 20,22 of adjoining die plate members 14 when these are stacked together andclamped together. Such sealing elements may include unitary gasketsreceived in a recessed zone surrounding the individual bores 20, 22.Hereagain, the competent cooling die tool maker has available to him/hera number of different options known in the art.

FIG. 1 illustrates one manner in which the die plate members 14 and thedistribution end plates 16, 18 can be clamped together to form a unitarycooling die body 12. To this end, a total of eight tie rods 30 areprovided. These extend parallel to one another and are evenly spacedabout the axis of the assembly. One of the threaded ends of tie rods 30screws into threaded fastening holes 31 provided at transition plate 15at the inlet side of cooling die assembly 10, whereas the other threadedend extends through holes in the distribution (end) plate 18 at theproduct outlet side of cooling die assembly 10 and are secured thereatusing nuts 32. This arrangement allows for clamping of the stacked plateassembly together in leak-tight manner.

Not illustrated in greater detail in FIG. 1, transition plate 15incorporates flow distribution means thereby to ensure that extrudatereceived from the extruder outlet is evenly distributed to the extrudateflow bores 20′ at the inlet distribution (end) plate 16 of cooling dieassembly 10. The extrudate distribution means are illustratedschematically at dotted line 33.

In use of the production facility, molten lava (i,e, extrudate) from theextruder flows through extruder outlet into attachment flange piece 13and through extrudate distributor (i.e. transition) plate 15 beforepassing though coolant distribution (end) plate 16 and entering thefirst of the cooling plate members 14. The flow of extrudate is evenlydistributed over all product channels 1 due to all product paths beingof similar lengths. However, if necessary, a restriction may be placedbetween transition plate 15 and the inlet-side cooling fluiddistribution plate 16 in order to induce a pressure drop. Thisrestriction is normally not required but may be added if even productflow from all channels is critical. Once the extrudate has entered thefirst of the stacked cooling plates 14 it conveys along the extrudateflow channels 20 formed by individual cooling plates attached togetherbefore exiting the cooling die via the outlet cooling fluid distributionplate 18. The total number of cooling plates 14 may be varied accordingto the heat transfer area required for the specific productThermocouples may be inserted into the cooling plates at speciallyprepared points if required, to control the process.

As mentioned previously a restriction plate may be used in conjunctionwith the cooling die assembly 10 so that overall product velocitydistribution is minimised. In a further development of the invention, acooling die extrusion plate having a plurality of discharge orifices canbe incorporated at the outlet end of the assembly. Molten, cooled-downlava is pressed through the orifices and, due to the pressure dropacross said plate, partially solidifies. Product produced from such anarrangement has a partially cut appearance caused by the breakup of themolten lava into multiple flow paths that are not able to reform into ahomogeneous mass downstream of the restriction plate. Product ensuingfrom the cooling die may subsequently be cut up by simple mechanicalcutting devices attached directly to the final face of the cooling die.The product produced is regular in size but irregular in shape andresembles quite closely places of cut neat.

FIGS. 4-8 illustrate different views of a cooling die in accordance withthe invention which incorporates a cooling die extrusion plate assemblyat the outlet end of the cooling die body thereby 10 enable extrusion ofdifferently shaped extrudates without the need for exchanging of thedischarge end plate. The cooling die assembly 10 is substantialitysimilar to that described with reference to the FIGS. 1-3 and,accordingly, the same reference numerals are used to denote similarcomponent parts. It will be noted that the inlet end of the cooling dieassembly 10 is located at the right hand side in the illustration ofFIG. 4 (instead of the left hand side in the illustration of FIG. 1).

The cooling die extrusion plate assembly is generally identified atreference numeral 50 in FIG. 4 and essentially consists of an annularsteel plate 51 (see FIGS. 6 and 7) incorporating a total of twenty-fourlong holes 52 and 54 which pass through the thickness 91 plate 51 andextend in a generally radial direction from the centre of plate 51.Shape, size and location of the discharge orifices 52, 54 ispredetermined by that present in die plate members 14 that make up thecooling die stack 12. Discharge orifices 52 and 54 are identical inshape but for the provision of an array of eleven mounting slots 55 thatextend perpendicular to the height (i.e. radial extension) of orifices54. These slots 55 are machined into one surface only of plate 51thereby to terminate with distance from the opposing surface. Theseslots 51 serve to receive in form, fitting manner non-illustratedcutting blades which traverse the orifice 54 and thereby subdivide itsmain extension into discrete radial lengths. Accordingly, whilstextrudate passing through orifices 52 will have a generally band-likecross-sectional shape, the presence of the cutting knives in dischargeorifices 54 will cut the extruding band into individual threads ofsubstantially square cross-section.

Extrusion die plate 51 is received in a multi-piece support assembly 60which is flanged to the outward facing side of the product discharge endof coolant distribution (end) plate 18 thereby to allow rotation ofdischarge plate 51 about the longitudinal axis of the coolingdie-extrusion die plate assembly. The respective location and relativepositioning of discharge orifices 52, 54 and the extrudate flow channels20′ at the end plate 18 is such that in a first position of theextrusion die plate 51 only extrusion orifices 52 will align withcorrespondingly associated ones of me extrudate flow channels 20 of thedie assembly 12, whereby, in the illustrated embodiment havingtwenty-four orifices 52, 54. half or them will allow passage ofextrudate through, whilst the other twelve will be offset with respectto the other extrudate flow channels 22 of the die assembly 10 and canbe shut. Accordingly, it is possible to change the shape of theextrudate ribbon by rotating the extrusion die plate 51 from a positionin which the discharge orifices with blades are online, to a positionwhere the “open” orifices 52 (i.e. those without tranversing blades) arein alignment with the discharge openings at the end plate of theassembly.

It will be appreciated that the rotatable extrusion die plate 51 can bearranged for manual displacement into its different operationalpositions, or, alternatively, a suitable motorised drive train mayprovide such positioning

FIGS. 5 and 6 illustrate at reference numeral 61 a mounting plate whichcarries a wheel mounting block 62 supporting an externally toothed wheel64 that runs in a wheel track 68 coupled to the extrusion die plate 51.This drive train is coupled to motor 68 which serves to positionextrusion die plate 51 in a selected one of its rotational positions.The construction drawings of FIGS. 4-8 otherwise provide details of thesupport structure employed in holding the extrusion die plate 51 inabutting relationship at the coolant distribution end plate 16 and thedrive train employed for automatically setting its rotational position.

EXAMPLE

A meat analogue chunk having a fibrous striated structural matrix andresembling tuna white meat was prepared using extrusion apparatus andthe cooling die of the present invention as follows.

The following ingredients were weighed out and blended in a ribbonblender for 2 to 4 minutes.

Ingredient % by weight Defatted soy flour 43.6 Vital wheat gluten 43Di-calcium phosphate 5 Flavourings 5 Vitamins/minerals 3.4

The blended mixture was then metered into a twin screw extruder at aflowrate of 550 kg/hr. Water was added to the powder in the feed sectionof the extruder at a flowrate of 450 kg/hr, The blend was then subjectedto shear and pressure within the extruder prior to exiting the extruderat a temperature of 130-140° C. The molten extrudate then entered themulti-channel cooling die, attached directly to the outlet of theextruder The multi-channel cooling die consisted of 24 individualcooling channels, each channel having cross-sectional dimensions ofapproximately 6-8 mm by 70-90 mm. The total length of each coolingchannel was 0.7-1.2 meters. Product exited to cooling die as continuousslabs with a moisture content of approximately 48-53% and a temperatureof between 90-100° C., Water was used to cool the product. It enteredthe cooling die at a temperature of between 5 and 15° C. via the coolingfluid distribution plate located closest to the product exit and flowedin a counter-current direction to the flow of product cooling waterexited the cooling die at a temperature of between 20 and 30° C.

This strategy removes the main limitations associated with themanufacture of high moisture extruded product at high outputs, namelylength of cooling die and cooling die cross-sectional design. Using acooling die incorporating multiple cooling channels, one is able to usea cross-sectional design that produces a product with the correct visualand physical characteristics. One is also able to fix the length of thecooling die to a figure that optimises pressure drop, heat transferarea, heat transfer rate and process performance. Once the configurationfor a single cooling die (or channel) is determined (based on thedesired visual and physical characteristics of the final product), thenumber of individual cooling channels required may then be determined bythe desired total output

The present invention has been described in connection with certainpreferred embodiments. Nevertheless the invention is not so limited andincludes modifications and adaptations within the meaning and scope ofthe invention described herein.

The Claims Defining the Invention are as Follows:
 1. A cooling die, foruse in the manufacture of high moisture extruded food products, saidcooling die including: an inlet end and an outlet end; a plurality ofplate members stacked in plane-parallel relationship thereby to define amain body portion of the cooling die between the inlet and outlet ends;a plurality of extrudate flow channels extending through the cooling diefrom the inlet end to the outlet end and defined by individual throughbores in each plate member that align when the plate members arestacked, each extrudate flow channel having a major dimension in adirection extending radially away from a longitudinal axis of thecooling die main body portion that is at least 2.5 times the width in atraverse direction of the channel; a plurality of cooling fluid flowchannels extending through the cooling die from the inlet end to theoutlet end and defined by individual through bores in each plate memberthat align when the plate members are stacked; means for connecting thecooling die to an outlet of a food extruder, a cooling fluid source anda cooling fluid receptacle; and product flow distribution means, locatedadjacent the inlet end, adapted to direct extrudate from the outlet ofthe food extruder into said extrudate flow channels.
 2. A cooling diefor extruding of high moisture extrudate food products, having a coolingdie body in which are defined a plurality of extrudate flow channelsextending between an inlet end of the cooling die that is attachable toan extruder and an outlet end for delivery of cooled-down extrudate, andcoolant cavities located in heat-exchanging communication with theextrudate flow channels and connectable to a source of coolant,characterised in that the cooling die body consist of a plurality ofthick plates having a plurality of first and second bores extendingbetween and opening at the planar surfaces of the thick plates, and inthat the plurality of thick plates are stacked plane-parallel andfastened together such that the openings of the first and second boresof adjoining plates are respectively aligned with one another, wherebythe first bores form said plurality of extrudate flow channels and thesecond bores form a plurality of discrete coolant channels extendingthrough the length of the cooling die body.
 3. A cooling die accordingto claim 1 or 2, wherein the plurality of said extrudate flow channelsare arranged parallel to one another and equidistantly spaced about thecentral axis of the die.
 4. A cooling die according to claim 3 having 24extrudate flow channels.
 5. A cooling die according to any one of claims1 or 2, wherein the radial height of each extrudate flow channel isbetween about 20 to 100 mm and the width of each channel is betweenabout 6 to 10 mm.
 6. A cooling die according to claim 5, wherein theheight of each extrudate flow channel is about 70 mm and the width isabout 8 mm.
 7. A cooling die according to any one of claims 1 or 2,wherein each extrudate flow channel has a substantially rectangular oroval cross-section.
 8. A cooling die according to claim 7, wherein theextrudate flow channels are of uniform cross-section along their length.9. A cooling die according to any one of claims 1 or 2, wherein thecoolant flow bores are interleaved between neighbouring extrudate flowchannels.
 10. A cooling die according to any one of claims 1 or 2,wherein the cooling die plate members are disc-shaped or multi-facedplaced in face to face abutting arrangement thereby to form said mainbody portion.
 11. A cooling die according to any one of claims 1 or 2,further including a die extrusion end plate with apertures, the dieextrusion plate located adjacent to the outlet end and adapted to impartto the extruded food products a cross-sectional shape corresponding tothe shape of the apertures of said die plate.
 12. A cooling dieaccording to claim 11, wherein the apertures of said die plate have aplurality of different cross-sectional shapes; at least one aperture ofa first cross-sectional shape is located in close proximity to at leastone aperture of a second cross-sectional shape; and said die plate isadapted for movement between a first position, in which at least one ofthe apertures of the first cross-sectional shape is in alignment with atleast one of said extrudate flow channels, and a second position, inwhich at least one of the apertures of the second cross-sectional shapeis in alignment with said at least one of said extrudate flow channels.13. A cooling die according to claim 12, wherein the apertures arelocated on the die plate such that, when in the first position,substantially all of the apertures of the first cross-sectional shapeare in alignment with corresponding extrudate flow channels, and when inthe second position, substantially all of the apertures of the secondcross-sectional shape are in alignment with said corresponding extrudateflow channels.
 14. A cooling die according to claim 12, wherein theapertures of the first cross-sectional shape are radially spaced fromapertures of the second cross-sectional shape.
 15. A cooling dieaccording to claim 14, wherein each of the apertures of the firstcross-sectional shape are arranged sequentially with the apertures ofthe second cross-sectional shape.
 16. A cooling die according to claim12, wherein the die plate includes at least one group of apertures ofthe first cross-sectional shape which is radially or peripherallyseparated from at least one group of apertures of the secondcross-sectional shape.
 17. A cooling die according to claim 12, whereinthe die plate is mounted to the cooling die for rotation about a centralaxis thereof.
 18. A cooling die according to claim 12, wherein theapertures of the first cross-sectional shape are elongated slits and theapertures of the second cross-sectional shape are elongated sifts havingcutting elements traversing said slits.
 19. A cooling die according toclaim 18, wherein the cutting elements are blades or wires mountedacross the respective slits in an arrangement so as to cut the extrudedfood product exiting the die plate into strips having a substantiallysquare cross-section.
 20. A cooling die according to any one of claims 1or 2, further including a cutting device arranged downstream of the dieplate and adapted for cutting extruded food product into desiredlengths.
 21. A cooling die according to claim 20, wherein the cuttingdevice includes a rotatable blade.
 22. A cooling die according to claim2, further including a coolant supply and a coolant discharge end plateat axially opposite ends of the cooling die body, wherein the end platesinclude manifold conduits for supplying or discharging coolant to/fromthe coolant channels of the die body, as the location of the end platesdictate.
 23. A cooling die according to claim 22, wherein there isincorporated an extrusion die plate at the outlet end of the cooling diebody downstream of the coolant discharge end plate, the extrusion dieplate having a plurality of discharge orifices of predetermined shapeand configuration that are grouped and arranged to be selectively boughtin axial alignment with predetermined ones of the extrudate flowchannels thereby to enable extrusion of cooled-down extrudate bandshaving selected ones of different cross-sectional shapes in accordancewith the discharge orifice shape.